Optical switch and display unit

ABSTRACT

The present invention provides an optical switch for making part of incident light, which has been made incident on an optical waveguide, selectively emergent to a light emergence portion provided outside the optical waveguide. The optical switch includes a liquid crystal device for selective emergence of the incident light. An arbitrary layer of the liquid crystal device is set such that letting Δn be a difference between a refractive index n 0  of the optical waveguide and a refractive index n 1  of the arbitrary layer of the liquid crystal device, “d” be a thickness of the arbitrary layer, and λ be a wavelength of the incident light, the values of Δn, “d”, and λ satisfy a condition of 2.20×10 −3 ≦|Δn·d·λ −1 |≦3.03×10 −3 . With this optical switch, the uniformity of a light emergence efficiency can be easily realized by making use of a small change region in which the light emergence efficiency is not largely varied. The present invention also provides a display unit using the optical switches.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an optical switch for makinglight in an optical waveguide selectively emergent therefrom, and adisplay unit on which the optical switches are arrayed.

[0002] In home televisions, a cathode-ray tube having a mechanism ofemitting light by exciting phosphors with electron beams is used as adisplay. In liquid crystal displays, a light transmittance is changed byvarying a polarization characteristic of liquid crystal. In these liquidcrystal displays, a color of white light is selected by using a filter.In plasma displays, phosphors are excited with ultraviolet raysgenerated by plasma.

[0003] By the way, television receivers have disadvantages that a depthof a cathode-ray tube is long, thereby making it impossible to realize athin display, and that the weight of the cathode-ray tube is heavy. Afurther disadvantage of the television receivers is that since lightemission is obtained by exciting phosphors, a half-width of an emissionspectrum of each of three primary colors is large, to degrade a colorpurity and a color reproducing characteristic. Liquid crystal displayshave a disadvantage that since a half-width of an emission spectrumdetermined by a color filter is also large, to degrade a color purityand a color reproducing characteristic. Plasma displays havedisadvantages that since light emission is obtained by excitingphosphors like cathode-ray tubes, a half-width of each emission spectrumis large, to degrade a color purity and a color reproducingcharacteristic, and that it is not easy to adjust gradation of an image.

[0004] On the other hand, as display units utilizing photonics, thereare known display units using optical waveguides. Such a display unit,however, has a problem that a contrast ratio of light emergent inresponse to turn-on/turn-off of an optical switching device, that is, anoptical switch such as liquid crystal is low. Further, an optical switchhaving a structure in which light transmissive layers are stacked hasanother problem that a slight change in light emergence efficiencydepending on a thickness and a refractive index of each layer of thestacked structure may exert a large effect on an uniformity of theentire light emergence efficiency, and therefore, it is expected toprovide an optical switch capable of easily realizing the uniformity ofa light emergence efficiency.

[0005] An optical switch composed of an optical waveguide including atleast a cladding layer, and a light directivity coupler having anelectrode film, an alignment control film, and ferroelectric liquidcrystal filled between a pair of substrates is known, for example, fromJapanese Patent Laid-open No. Hei 8-36196. The design of this opticalswitch aims that a coupling efficiency (light emergence efficiency)becomes 1, that is, a transfer rate of light becomes 100% by optimizinga refractive index of liquid crystal, and with respect to such design ofthe optical switch, the above document describes that the couplingefficiency can reach 98% by setting an effective refractive index ofliquid crystal to 1.523.

[0006] An optical switch designed to pursue a high coupling efficiencyas the optical switch described in the above document, however, has aproblem. Namely, a refractive index of each component such asferroelectric liquid crystal, an optical waveguide, an electrode film,or an alignment control film may be deviated from a design value due tovariations which occur depending on a thickness and a materialcharacteristic of each layer in production steps, and if the refractiveindex of a component is deviated from a design value, then such adeviation cannot be canceled only by adjusting a refractive index offerroelectric liquid crystal, and the coupling efficiency is largelydegraded as the deviation in the refractive index of the component fromthe design value becomes large, thereby failing to obtain the uniformityof a light emergence efficiency.

SUMMARY OF THE INVENTION

[0007] An object of the present invention is to provide an opticalswitch capable of significantly improving a contrast ratio, obtaining aclear, bright image, and easily realizing the uniformity of a lightemergence efficiency, and to provide a display unit using the opticalswitches.

[0008] To achieve the above object, according to a first aspect of thepresent invention, there is provided an optical switch for making partof incident light, which contains a specific polarized light componentand has been made incident on an optical waveguide, selectively emergentfrom the optical waveguide to a light emergence portion provided outsidethe optical waveguide, the optical switch including: a multi-layerstructure composed of a plurality of light transmissive layer; whereinletting U be a refractive index control accuracy at the time ofproducing the multi-layer structure, a refractive index of at least onelight transmissive layer in the multi-layer structure is different froma refractive index of a light transmissive layer other than the at leastone light transmissive layer in the multi-layer structure by 3σ or more.

[0009] According to a second aspect of the present invention, there isprovided an optical switch for making part of incident light, whichcontains a specific polarized light component and has been made incidenton an optical waveguide, selectively emergent from the optical waveguideto a light emergence portion provided outside the optical waveguide, theoptical switch including: a light transmissive stacked structureincluding a function layer for selective emergence of the incidentlight; wherein letting Δn be a difference between a refractive index n₀of the optical waveguide and a refractive index n₁ of an arbitrary layerforming part of the stacked structure, “d” be a thickness of thearbitrary layer, and λ be a wavelength of the incident light, the valuesof Δn, “d”, and λ satisfy a condition of 2.20×10⁻³≦|Δn·d·⁻¹|<03×10⁻³.

[0010] According to the second aspect of the present invention, there isalso provided a display unit including: a plurality of opticalwaveguides, disposed approximately in parallel to each other, forreceiving light containing a specific polarized light component asincident light; one or two or more light emergence portions crossing theoptical waveguides; and optical switches, disposed between thewaveguides and the light emergence portions, for making part of theincident light selectively emergent from the optical waveguides to thelight emergence portions provided outside the optical waveguides;wherein each of the optical switches has a light transmissive stackedstructure including a function layer for selective emergence of theincident light; and letting Δn be a difference between a refractiveindex n₀ of the optical waveguide and a refractive index n₁ of anarbitrary layer forming part of the stacked structure, “d” be athickness of the arbitrary layer, and λ be a wavelength of the incidentlight, the values of Δn, “d”, and λ satisfy a condition of2.20×10⁻³≦|Δn·d·λ⁻¹|≦3.03×10⁻³.

[0011] With these configurations of the second aspect of the presentinvention, in which a value of Δn·d·λ⁻¹ is specified, even if arefractive index of each layer of the light transmissive stackedstructure of the optical switch is fluctuated, the light emergenceefficiency is not varied so much. To be more specific, as a result ofcalculation, it is revealed that a small change region, in which thelight emergence efficiency is not largely changed even if the refractiveindex n₁ of an arbitrary layer is fluctuated and is somewhat deviatedfrom a design value, is present in the vicinity of a refractive indexportion at which the light emergence efficiency is maximized. By makingeffective use of such a small change region, it is possible to suppressa variation in light emergence efficiency even if the refractive indexof an arbitrary layer is varied. The small change region in which thelight emergence efficiency is not largely changed appears under acondition that a deviation in phase of light passing through anarbitrary layer (refractive index: n1, and thickness: “d”) is within aspecific range. A value of Δn·d·λ⁻¹ expresses the deviation in phase oftransmission light, and the above condition for suppressing the lightemergence efficiency by making use of the small change region is givenby an expression of 2.20×10⁻³≦|Δn·d·λ⁻¹|≦3.03×10⁻³. The uniformity ofthe light emergence efficiency can be realized by setting the arbitrarylayer under the above condition.

[0012] According to a third aspect of the present invention, there isprovided an optical switch for making part of incident light, whichcontains a specific polarized light component and has been made incidenton an optical waveguide, selectively emergent from the optical waveguideto a light emergence portion provided outside the optical waveguide, theoptical switch including: a light transmissive stacked structureincluding a function layer for selective emergence of the incidentlight; wherein letting L μm be a length of the function layer in thelongitudinal direction of the optical waveguide, a thickness of theoptical waveguide is in a range of 0.05·L μm to 0.2·L μm.

[0013] According to the third aspect of the present invention, there isalso provided a display unit including: a plurality of opticalwaveguides, disposed approximately in parallel to each other, forreceiving light containing a specific polarized light component asincident light; one or two or more light emergence portions crossing theoptical waveguides; and optical switches, disposed between thewaveguides and the light emergence portions, for making part of theincident light selectively emergent from the optical waveguides to thelight emergence portions provided outside the optical waveguides;wherein each of the optical switches has a light transmissive stackedstructure including a function layer for selective emergence of theincident light; and letting L μm be a length of the function layer inthe longitudinal direction of the optical waveguide, a thickness of theoptical waveguide is in a range of 0.05·L μm to 0.2·L μm.

[0014] With these configurations of the third aspect of the presentinvention, in which a thickness of an optical waveguide is specified, alight intensity at one optical switch or at one pixel can be set to ahigh value. To be more specific, if the thickness of the opticalwaveguide is excessively thin as compared with a size of a functionlayer for selective emergence of the incident light in the opticalswitch, a mode number of a spectrum of light allowed to enter theoptical waveguide is reduced, so that it is difficult to obtain asufficient light intensity. On the other hand, if the thickness of theoptical waveguide is excessively thick as compared with the size of thefunction layer, the probability that a light ray of one mode enters thefunction layer of one optical switch is reduced, so that it isimpossible to obtain a sufficient light intensity even by performingselective emergence of light. Accordingly, to optimize the lightintensity, it may be desirable to specify a range of the thickness ofthe optical waveguide. To be more specific, letting L μm be a length ofthe function layer in the longitudinal direction of the opticalwaveguide, the thickness of the optical waveguide may be set in a rangeof 0.05 L μm to 0.2 L μm in order to optimize the light intensity.

[0015] According to a fourth aspect of the present invention, there isprovided an optical switch for making part of incident light, whichcontains a specific polarized light component and has been made incidenton an optical waveguide, selectively emergent from the optical waveguideto a light emergence portion provided outside the optical waveguide, theoptical switch including: a light transmissive stacked structureincluding a function layer for selective emergence of the incidentlight; wherein letting Δn be a difference between a refractive index n₀of the optical waveguide and a refractive index n₁ of an arbitrary layerforming part of the stacked structure, “d” be a thickness of thearbitrary layer, and λ be a wavelength of the incident light, the valuesof Δn, “d”, and λ satisfy a condition of |Δn·d·λ⁻¹|≦3.03×10⁻³ and|Δn·d·λ⁻¹|≠0.

[0016] With this configuration of the fourth aspect of the presentinvention, since the range of a deviation in phase of transmissionlight, which is expressed by Δn·d·λ⁻¹, is extended, the production of anoptical switch becomes easier than the production of the optical switchunder the above-described condition specified according to the secondaspect of the present invention. In addition, since a value of Δn maybecome negative, the deviation in phase of transmission light isexpressed by an absolute value of Δn·d·λ⁻¹.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a schematic perspective view showing a structure of anoptical switch according to a first embodiment of the present invention;

[0018]FIG. 2 is a schematic perspective view showing a structure of adisplay unit using the optical switches according to the firstembodiment of the present invention;

[0019]FIG. 3 is a typical sectional view showing a cross-sectionalstructure of the optical switch according to the first embodiment of thepresent invention;

[0020]FIG. 4 is a graph showing a relationship between a supplementaryangle and a reflectance in the optical switch according to the firstembodiment of the present invention;

[0021]FIG. 5 is a graph showing a relationship between a refractiveindex of a transparent electrode and a light emergence efficiency in theoptical switch according to the first embodiment of the presentinvention;

[0022]FIG. 6 is a graph showing a relationship between a refractiveindex of liquid crystal and a light emergence efficiency in the opticalswitch according to the first embodiment of the present invention;

[0023]FIG. 7 is a typical view illustrating a phase difference of anoptical switch structure;

[0024]FIGS. 8A and 8B are schematic sectional views each showing anoptical waveguide and an optical switch structure according to a secondembodiment of the present invention;

[0025]FIG. 9 is a graph showing a relationship between a light intensityand a supplementary angle in an optical waveguide according to thesecond embodiment of the present invention;

[0026]FIG. 10 is a graph showing a relationship between a supplementaryangle and a mode number in the case where laser light is made incidenton an optical waveguide according to the second embodiment of thepresent invention;

[0027]FIG. 11 is a graph showing a relationship between a mode numberand a thickness of an optical waveguide in the case where laser light ismade incident on the optical waveguide according to the secondembodiment of the present invention;

[0028]FIG. 12 is a graph showing a relationship between a lightintensity and a thickness of an optical waveguide in the case wherelaser light is made incident on the optical waveguide according to thesecond embodiment of the present invention; and

[0029]FIG. 13 is a graph showing a relationship between a systemefficiency and a thickness of an optical waveguide in the case wherelaser light is made incident on the optical waveguide according to thesecond embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] An optical switch and a display unit using the optical switchesaccording to the present invention will be hereinafter described indetail with reference to the accompanying drawings, in which preferredembodiments are shown.

[0031] According to a first embodiment, there is provided an opticalswitch for making part of incident light, which contains a specificpolarized light component and has been made incident on an opticalwaveguide, selectively emergent from the optical waveguide to a lightemergence portion provided outside the optical waveguide. The opticalswitch includes a multi-layer structure composed of a plurality of lighttransmissive layer. In this optical switch, letting σ be a refractiveindex control accuracy at the time of producing the multi-layerstructure, a refractive index of at least one light transmissive layerin the multi-layer structure is different from a refractive index of alight transmissive layer, other than said at least one lighttransmissive layer in the multi-layer structure, by 3σ or more.

[0032] According to the first embodiment, there is also provided anoptical switch for making part of incident light, which contains aspecific polarized light component and has been made incident on anoptical waveguide, selectively emergent from the optical waveguide to alight emergence portion provided outside the optical waveguide. Theoptical switch includes a light transmissive stacked structure includinga function layer for selective emergence of the incident light. In thisoptical switch, letting Δn be a difference between a refractive index n₀of the optical waveguide and a refractive index n₁ of an arbitrary layerforming part of the stacked structure, “d” be a thickness of thearbitrary layer, and λ be a wavelength of the incident light, the valuesof Δn, “d”, and λ satisfy a condition of 2.20×10⁻³≦|Δn·d·λ⁻¹|≦3.03×10⁻³.

[0033] The optical switch in this embodiment is provided with an opticalwaveguide, and if a display unit is composed of a plurality of theoptical switches, then a plurality of optical waveguides, each of whichis formed into a flat plate shape, are arrayed.

[0034]FIG. 1 is a typical perspective view showing a structure of anoptical switch. An optical waveguide 1 is formed of a plate-like membermade from a polycarbonate based resin. Light emitted from a light source6 such as a semiconductor laser is made incident on an end face 12 ofthe optical waveguide 1. The optical waveguide 1 crosses a lightemergence portion 2 formed into a flat-plate shape like the opticalwaveguide 1. At a portion where the optical waveguide 1 crosses thelight emergence portion 2, a liquid crystal device 3 is held between theoptical waveguide 1 and the light emergence portion 2.

[0035] The light source 6 used for the optical switch 10 is not limitedto the above-described semiconductor laser but may be an LED (LightEmitting Diode) light source or an EL (Electroluminescence) lightsource. In the case of using light containing a specific polarized lightcomponent, a sheet polarizer may be used. The above-described lightsource is advantageous in that a half-width of an emission spectrum isrelatively small and thereby a color purity is excellent. Accordingly,the use of such a light source is effective to produce a desirable threeprimary color display unit.

[0036] The optical waveguide 1 may be made from a light transmissivematerial having desired rigidity, flexibility, and heat resistance, forexample, a polycarbonate based resin. The material for the opticalwaveguide 1, however, is not limited thereto but may be any othertransparent synthetic resin or quartz glass. In this embodiment, theoptical waveguide 1 is formed into an elongated flat plate shape. Theshape of the optical waveguide 1, however, is not limited thereto butmay be a round bar shape or a square bar shape. The optical waveguide 1may be configured as optical fibers.

[0037] The liquid crystal device 3 formed between the optical waveguide1 and the light emergence portion 2 has a function layer for selectiveemergence of incident light. An operational mode of the function layercan be selectively changed into either a total reflection mode forallowing total reflection of incident light in the optical waveguide 1or an emission mode for allowing emission of incident light via theliquid crystal device 3. The selective control of the liquid crystaldevice 3 is performed by changing a voltage 5 applied to the liquidcrystal device 3. In the emission mode, the waveguided light emergesupward from an upper surface of the liquid crystal device 3. To increasean light emergence efficiency from the liquid crystal device 3, agrating 7 is mounted on the upper surface of the light emergence portion2. The liquid crystal device 3 has a light transmissive stackedstructure (which will be described later), and is operated for selectiveemergence of incident light. It is to be noted that the device having afunction layer, used for the optical switch in this embodiment, is notlimited to the liquid crystal device 3 but may be one kind or acombination of two or more kinds selected from a group consisting oflayers capable of, depending on a change in electric field or light,modulating a refractive index, a refractive index distribution, anemission intensity, a color density, a dielectric constant, and apermeability, and layers capable of, depending on a change in electricfield or light, changing a liquid crystal alignment state, andscattering light. Such a device having a function layer allows selectiveemergence or cutoff of light. In particular, in the case of using theliquid crystal device 3 as the device having a function layer of theoptical switch as in this embodiment, the liquid crystal device 3 may bedesirable to have ferroelectric liquid crystal.

[0038]FIG. 2 shows a flat type display unit 20 including opticalswitches arrayed within a flat plane. A plurality of optical waveguides11 typically made from polycarbonate resin extend in the horizontaldirection within a flat plane in such a manner as to be spaced from eachother at specific intervals, and a plurality of flat plate shaped narrowlight emergence portions 12 extend in such a manner as to cross theoptical waveguides at right angles. Liquid crystal devices 13 aredisposed at portions where the plurality of optical waveguides 11 crossthe plurality of light emergence portions 12. The liquid crystal device13 has a function layer for selective emergence of incident light. Anoperational mode of the liquid crystal device 13 can be selectivelychanged into either a total reflection mode for allowing totalreflection of incident light in the optical waveguide 11 or an emissionmode for allowing emission of incident light via the liquid crystaldevice 13 by changing a voltage 15 applied to the liquid crystal device13.

[0039] An approximately flat plate shaped base 19 is mounted on a baseend side of each optical waveguide 11, and each of semiconductor lasers16, 17 and 18 corresponding to respective emission colors is mounted onan upper surface of the base 19 in such a manner that the emission sideof the semiconductor laser is directed toward an end face of thecorresponding optical waveguide 11. A lens 14 is provided between eachof the semiconductor lasers 16, 17 and 18 and the end face of thecorresponding optical waveguide 11. Laser light emitted from each of thesemiconductor lasers 16, 17 and 18 is made incident on the end face ofthe corresponding optical waveguide 11 via the lens 14. Thesemiconductor lasers 16, 17 and 18 corresponding to respective emissioncolors are typically configured as lasers capable of emitting laserlight of red, green and blue in this order, and the optical waveguides11 corresponding to the semiconductor lasers 16, 17 and 18 waveguide theincident laser light of red, green and blue, respectively. For example,by arraying 4,800 pieces of the optical waveguides in the horizontaldirection on a display screen and arraying 1,200 pieces of lightemergence portions in the vertical direction on the display screen, afull color display unit having 1,920,000 pixels can be realized.

[0040] As a preferred example of the semiconductor laser or lightemitting diode used for the present invention, an AlGaInP based groupIII-V semiconductor light emitting device is used as a red light source,a ZnSe based group II-VI semiconductor light emitting device or a GaNbased group III-V semiconductor light emitting device is used as a greenlight source, and a ZnSe based group II-VI semiconductor light emittingdevice or a GaN based group III-V semiconductor light emitting device isused as a blue light source. Further, as a preferred example of anelectroluminescence light emitting device used for the presentinvention, a ZnS based light emitting device is used as each of a redlight source, a green light source, and a blue light source.

[0041] The use of a soft material such as a plastic material as adisplay unit forming material can realize display units of the opticalwaveguide type which have various sizes from a large size to a compactsize, for example, a curved display having a punchy screen spread at awide angle of typically 120°, a semi-spherical display, a full-sphericaldisplay, a cocoon type display, and a display allowed to be hoisted notat the time of use.

[0042] An essential structure of a liquid crystal type optical switchaccording to this embodiment will be described with reference to FIG. 3.As shown in FIG. 3, the essential structure of the liquid crystal typeoptical switch includes a stacked structure in which a liquid crystaldevice is held between an optical waveguide 31 and a light emergenceportion 32. To be more specific, alignment films 34 and 36 are formedbetween transparent electrode layers 33 and 37, and a liquid crystallayer 35 is formed between the alignment films 34 and 36. Each of theoptical waveguide 31 and the light emergence portion 32 is, as describedabove, typically made from a light transmissive polycarbonate basedresin, and in this case, a refractive index n₀ thereof is set to 1.585.Each of the transparent electrode layers 33 and 37 is made fromtypically an ITO film, and in this case, a refractive index thereof isset to the same value as that of the optical waveguide 31, that is,1.585. However, as will be described later, according to the structurein this embodiment, even if the refractive index of each of thetransparent electrode layers 33 and 37 is somewhat deviated from asetting value, the light emergence efficiency is not reduced. Athickness of each of the transparent electrodes 33 and 37 is typicallyset to 0.50 μm. A mode of the liquid crystal layer 35 is selected inresponse to a voltage applied between the transparent electrode layers33 and 37.

[0043] The alignment layers 34 and 36, each of which is typically madefrom a polyimide based resin, are formed on the transparent electrodelayer 33 and under the transparent electrode layer 37, respectively. Arefractive index of each of the alignment films 34 and 36 is set to belarger than the refractive index n₀ of each of the optical waveguide 31and the light emergence portion 32 by a value of about 0.05 to 0.15. Ingeneral, a refractive index of a glass material is controlled at anaccuracy of five decimal places, and a refractive index of an organicmaterial such as a synthetic resin is controlled at an accuracy of fourdecimal places. Letting σ be a refractive index control accuracy at thetime of producing the multi-layer structure, a value of 3σ is in theorder of three decimal places at maximum, and accordingly, a deviationof a refractive index in a range of about 0.05 to 0.15 largely exceedsthe value of 3σ, that is, largely exceeds an error range at the time ofproducing the multi-layer structure. A thickness of each of thealignment films 34 and 36 is set to 0.142 μm.

[0044] The liquid crystal layer 35 is a function layer for selectivetransmission of incident light, and a reflectance of the liquid crystallayer 35 is largely changed in response to a voltage applied between thetransparent electrode layers 33 and 37. In this embodiment,ferroelectric liquid crystal is used for the liquid crystal layer 35,and in the ON state of the liquid crystal, light in the opticalwaveguide 31 reaches the light emergence layer 32, and in the OFF stateof the liquid crystal, light in the optical waveguide 31 is cutoff bythe liquid crystal layer 35 and thereby the light does not reach thelight emergence layer 32. FIG. 4 shows a reflectance R of the liquidcrystal layer. In a range of a supplementary angle θ (to a reflectionangle) of 20° or less, in the OFF state of liquid crystal, thereflectance R of the liquid crystal layer becomes a value closer to anapproximately 1, and in the ON state of liquid crystal, the reflectanceR of the liquid crystal layer becomes 0.2 or less, that is,substantially zero.

[0045] The feature of the optical switch in this embodiment lies in thateven if a refractive index and a thickness of an arbitrary layer aredeviated, a light emergence efficiency can be uniformly retained. Thisfeature will be described below. Since the optical switch in thisembodiment has the structure in which respective light transmissivelayers are stacked, refractive indexes of these layers exert effects ona light emergence efficiency of the entire optical switch. The conditionunder which the efficiency is maximized, that is, the light emergenceefficiency η is set to 1 can be established by making a refractive indexof each of the layers identical to the refractive index n₀ of theoptical waveguide. Such a condition is effective to design an opticalswitch capable of maximizing the light emergence efficiency. Theadoption of such a maximum efficiency condition, however, causes aproblem. Namely, under a condition closer to the maximum efficiencycondition that the light emergence efficiency η becomes 1, even if arefractive index of a layer is slightly deviated from a design value,the light emergence efficiency η is largely deviated from 1. As aresult, for a display unit on which optical switches are arrayed withina flat plane, variations between the optical switches becomesignificantly large. To cope with such a problem, according to thisembodiment, in place of adopting a maximum efficiency portion for astacked structure of an optical switch, a small change region closer tothe maximum efficiency portion, in which the light emergence efficiencyη is not largely changed even if a refractive index of a layer isdeviated, is positively utilized for a stacked structure of an opticalswitch.

[0046]FIG. 5 is a graph showing a change in light emergence efficiency ηdepending on a deviation in refractive index of a transparent electrode.As is apparent from this graph, each of four curves has theabove-described small change region. In addition, data shown in thegraph are obtained for the same structure as that shown in FIG. 3, inwhich a transparent electrode layer having a refractive index “n”, andan alignment film having a refractive index PI are formed on an opticalwaveguide having a refractive index n₀. More specifically, the fourcurves show the data for the four structures in which the refractiveindexes PI of the alignment film are 1.593, 1.594, 1.595, and 1.596,respectively. In the graph, the ordinate designates the light emergenceefficiency η and the abscissa designates the refractive index “n” of thetransparent electrode layer. In each of the four curves shown in FIG. 5,the small change region, in which even if the refractive index “n” isvaried, the light emergence efficiency η is not largely changed, ispresent in a range which is larger than the refractive indexcorresponding to the maximum efficiency by about 0.002. An opticalswitch using such a small change region makes it possible to suppress avariation in light emergence efficiency η even if the refractive index“n” is varied, and a display unit capable of keeping the uniformity ofthe light emergence efficiency η can be obtained by using such opticalswitches.

[0047] Like the example shown by the graph in FIG. 5 in which therefractive index of the transparent electrode is deviated, a smallchange region is present in which even if a refractive index of a liquidcrystal layer is deviated, the light emergence efficiency η is notlargely changed. FIG. 6 shows a change in light emergence efficiency ηdepending on a variation in refractive index of the liquid crystallayer. As shown in FIG. 6, in a range of a refractive index of analignment film from 1.565 to 1.610, a small change region SD, in whichthe light emergence efficiency η is not largely changed, is present onthe side slightly smaller than the refractive index corresponding to themaximum efficiency. An optical switch using such a small change regionmakes it possible to suppress a variation in light emergence efficiencyη even if the refractive index of the liquid crystal layer is varied,and a display unit capable of keeping the uniformity of the lightemergence efficiency η can be obtained by using such optical switches.

[0048] The condition under which such a small change region appears willbe more fully described below. In general, the light emergenceefficiency η is not determined only by a deviation from the perfectstructure composed of all layers whose refractive indexes are perfectlyidentical to each other, but is determined by the deviation inrefractive index of a layer multiplied by a thickness of the layer. Tobe more specific, a value obtained by dividing a product of a deviationin refractive index Δn (=n₀−n₁) and a thickness “d” by a wavelength λbecomes a deviation in phase α, and the deviation in phase α determinesthe reflectance and the light emergence efficiency η. This is typicallyshown in FIG. 7. Referring to this figure, light passes through twomedia 41 and 42. In this case, assuming that an intermediate portion 43of the medium 41 has a thickness “d” and a refractive index n₁ and anintermediate portion 44 of the medium 42 has a thickness “d” and arefractive index n₀, a phase difference caused by transmission of lightthrough the media 41 and 42 having different refractive indexes isexpressed by d·Δn·λ⁻¹. Such a phase difference d·Δn·λ⁻¹ becomes a factordetermining the light emergence efficiency η.

[0049] On the other hand, as a result of a plurality of simulation testscarried by the present inventors, it is revealed that d·Δn=1.278×10⁻³ μmbecomes a condition under which the above-described small change regionappears. Hereinafter, a condition under which the above-described smallchange region appears will be more fully described by using the datashown in FIG. 5. FIG. 5 shows the result which is calculated with thewavelength λ fixed at 0.515 μm, the thickness “d” of the alignment filmfixed at 0.142 μm, and the refractive index n0 of the optical waveguidefixed at 1.585, and the refractive index nPI of the alignment filmvaried in a range of 1.593 to 1.596. Accordingly, in the case of therefractive index nPI=1.593, Δn (=nPI−n0) becomes 0.008, with a resultthat d·Δn·λ⁻¹ becomes 2.20×10⁻³ and in the case of the refractive indexnPI=1.596, Δn (=nPI−n0) becomes 0.011, with a result that d·Δn·λ⁻¹becomes 3.03×10⁻³. Consequently, a condition of2.20×10⁻³≦|Δn·d·λ⁻¹|≦3.03×10⁻³ is obtained. In other words, by settingthe refractive index “n” and the thickness “d” of the transparentelectrode layer, and further the wavelength λ of transmission lightunder the condition of 2.20×10⁻³>Δn·d·λ⁻¹|≦3.03×10⁻³, the above smallchange region appears. As a result, it is possible to obtain the lightemergence efficiency η not largely changed even if the refractive index“n” of the transparent electrode layer is varied. Concretely, as shownby the data in FIG. 5, by satisfying the condition of2.20×10⁻³≦|Δn·d·λ⁻¹|≦3.03×10⁻³, the light emergence efficiency η islittle changed even if the refractive index of the transparent electrodeis deviated from 1.585 by a value of about ±0.0015. In addition, sincethe value of Δn may becomes negative, the deviation in phase oftransmission light is expressed by the absolute value of Δn·d·λ⁻¹.

[0050] In the above example, the condition of the transparent electrodelayer, under which the small change region can be obtained, iscalculated with the refractive index of the alignment film taken as aparameter. The same consideration can be applied to the liquid crystallayer. That is to say, by setting the liquid crystal layer under thecondition of 2.20×10⁻³≦|Δn·d·λ⁻¹|≦3.03×10⁻³, a small change regionappears. As a result, it is possible to obtain the light emergenceefficiency η not largely changed even if the refractive index of theliquid crystal layer is varied. For example, it is revealed that bysetting, at the wavelength of 0.515 μm, the refractive index of thealignment film to be higher than the refractive index of the opticalwaveguide by about 0.01, a small change region in which the lightemergence efficiency η is not largely changed appears. In this case,even if the refractive index of the liquid crystal layer is changed from1.582 to 1.585, a variation in light emergence efficiency η can besuppressed to a value of 2% or less.

[0051] The transparent electrode is not limited to the above-describedITO film but may be a fine particle dispersion type transparentelectrode film. The fine particle dispersion type transparent electrodefilm is a conductive film obtained by mixing a high refractive indexmaterial such as SnO₂ fine particles with a low refractive indexmaterial such as a polyester based resin. To control a refractive indexof the conductive film, it is required to mix the SnO₂ fine particleswith the polyester based resin at a specific mixing ratio For example, arefractive index n1 of the SnO₂ fine particles is 2.0, and a refractiveindex n2 of the polyester based resin is 1.45. In this case, arefractive index n3 of the mixture of the two kinds of materials isdetermined by a volume ratio “k” of the materials. Here, letting V1 bethe total volume of the fine particles and V2 be the total volume of thepolyester based resin, the volume ratio “k” becomes k=V1/(V1+V2) Therefractive index n3 of the mixture thus becomes n3=k×n1+(1−k)×n2. As aresult, for example, to set the refractive index n3 to 1.585, “k” mustbe set to 0.2455. In this case, if the volume V1 of the fine particlesis set to 10 mL, the volume V2 of the polyester based resin becomes30.73 mL.

[0052] In this way, a designed refractive index of the mixture isobtained by mixing the fine particles with the resin at a specificvolume ratio. This method can be applied to a combination of othermaterials. Since a refractive index of a mixture is determined by avolume ratio, even if the mixture is composed of not two kinds but threeor more kinds of materials, a desired refractive index of the mixturecan be obtained in accordance with the same manner. According to thisembodiment, even if a refractive index of a transparent electrode filmis somewhat varied, a variation in light emergence efficiency η can besuppressed, and consequently, the fine particle dispersion typetransparent electrode film produced by mixing a high refractive indexmaterial with a low refractive index material at a specific volume ratiois significantly effective.

[0053] The refractive index n₀ of the optical waveguide 31 shown in FIG.3 is not limited to 1.585 but may be more generalized. For example, therefractive index n₀ may be set to a value in a range of 1.57 to 1.60. Onthe optical waveguide 31 having the refractive index n₀ ranging from1.57 to 1.60, at least one layer or two layers each having a refractiveindex ranging from 1.594 to 1.595 and a thickness ranging from 0.13 μmto 0.16 μm may be formed as the alignment film 34 and 36 or thetransparent electrode layers 33 and 37. Further, the above-describedcondition of 2.20×10⁻³≦|Δn·d·λ⁻¹|≦3.03×10⁻³ may be replaced with acondition of |Δn·d·λ⁻¹|≦3.03×10⁻³ and |Δn·d·λ⁻¹|≠0. Under the conditionof |Δn·d·λ⁻¹|≦3.03×10⁻³ and |Δn·d·λ⁻¹|≠0, since a deviation in phase oftransmission light expressed by Δn·d·λ⁻¹ is extended, the production ofan optical switch becomes easier than the production of the opticalswitch under the condition of 2.20×10⁻³≦|Δn·d·λ⁻¹|≦3.03×10⁻³. Inaddition, since a value of Δn may become negative, the deviation inphase of transmission light is expressed by an absolute value ofΔn·d·λ⁻¹.

[0054] According to the optical switch and the display unit using theoptical switches in this embodiment, even if a refractive index of anarbitrary layer of a stacked structure constituting the optical switchis varied, a uniform light emergence efficiency η can be obtained bysetting the arbitrary layer such that the arbitrary layer satisfies aspecific condition. The specific condition is established by setting thephase difference Δn·d·λ⁻¹ of transmission light in a specific range. Inparticular, since the condition is dependent on λ⁻¹, that is, theinverse of the wavelength of transmission light, the structure of theoptical switch is also dependent on the wavelength of transmissionlight. Accordingly, in the case of producing a display unit using theoptical switches in this embodiment, as shown in FIG. 2, the wavelengthof light used is determined for each optical waveguide, and the opticalswitches corresponding to the light emitting devices for emission ofred, green and blue are disposed so as to correspond to the opticalwaveguides. In other words, in a full color display unit, opticalwaveguides for waveguiding light of different colors are arrayed, andeach of the optical switches, which is different from that adjacentthereto in terms of at least one of a thickness and a refractive indexof a layer forming the optical switch, is provided so as to correspondto a wavelength of light emitted from each light emitting device. Forexample, in an optical switch for receiving light of red, since thewavelength of the light of red is longer than that of light of blue, athickness of a layer forming the optical switch may be made thicker thana layer forming an optical switch for receiving light of blue. With thisconfiguration, it is possible to extend the uniformity over the screen.

[0055] A second embodiment of the present invention will be describedwith reference to FIGS. 8A and 8B, 9, 10, 11 and 12. In this embodiment,it is intended to optimize a size of an optical switch as well as a sizeof an optical waveguide. FIGS. 8A and 8B shows a state in which lighthaving been made incident on an optical waveguide emerges from oneoptical switch.

[0056] Referring to FIGS. 8A and 8B, an end face of a semiconductorlaser 51, which functions as a semiconductor light emitting device, isin close-contact with an end face of an optical waveguide 52, and laserlight (TE mode) emitted from the semiconductor laser 51 is made incidenton the optical waveguide 52. A plurality of liquid crystal switches 53a, 53 b, 53 c and 53 d, which function as optical switches, are arrayedon the optical waveguide 52. Each of the liquid crystal switches 53 a to53 d is independently switched between an ON state and an OFF state inresponse to a voltage applied from a drive circuit (not shown) thereto.In the examples shown in FIGS. 8A and 8B, only the liquid crystal switch53 c is in the ON state and the other liquid crystal switches 53 a, 53 band 53 d are in the OFF states. Each of the liquid crystal switches 53 ato 53 d transmits light in the ON state and cuts off light in the OFFstate.

[0057]FIG. 8A typically shows the case where a quantity of light allowedto emerge from the liquid crystal switch 53 c in the ON state is small.Reversely, FIG. 8B typically shows the case where a quantity of lightallowed to emerge from the liquid crystal switch 53 c in the ON state islarge. To produce a high-intensity display unit, liquid crystal switchesused for the display unit may be configured so as to increase a quantityof light allowed to emerge from those, in the ON state, of the liquidcrystal switches as shown in FIG. 8B.

[0058] With respect to laser light emitted from the semiconductor laser51, as shown in FIG. 9, a light intensity (I) in the optical waveguideon the ordinate is dependent on an incident supplementary angle θ andexhibits a Gauss distribution with a relatively narrow half-width. Inthe light intensity distribution shown in FIG. 9, a mode number issequentially increased in the order of a first order mode, a secondorder mode, a third order mode . . . from a small angle θ portiondepending on the angle θ. That is to say, the mode number becomes largeras the angle θ becomes larger. FIG. 10 shows data in an opticalwaveguide system, wherein the ordinate designate an incidentsupplementary angle θ and the abscissa designates a mode number. As isshown in the figure, as a thickness of an optical waveguide becomesthick, the mode number becomes large along with an increase in angle θ.

[0059]FIG. 11 shows a relationship between a thickness “d” of an opticalwaveguide and a mode number. The mode number of laser light traveling inthe optical waveguide is increased linearly with the thickness “d” ofthe optical waveguide. For example, when the thickness “d” of theoptical waveguide exceeds 50 μm, the mode number exceeds 100, and inthis case, a sufficient light intensity can be obtained. However, whenthe thickness “d” of the optical waveguide exceeds 200 μm, although themode number is further increased, the light intensity is littleincreased. That is to say, in this case, the increase in mode numberdoes not contribute to an increase in light intensity. FIG. 12 shows acalculation result of a light intensity of laser light of the TE mode,which has been made incident on an optical waveguide and is made toemerge from the optical waveguide via one optical switch having a lengthof 1 mm in the longitudinal direction of the optical waveguide,depending on a variable thickness “d” of the optical waveguide. Thevariable thickness “d” is selected from 10, 50, 100, 200, 300, and 600μm. As shown in FIG. 12, when the thickness “d” of the optical waveguideexceeds 200 μm, the light intensity is little increased. This means thatwhen the thickness “d” of the optical waveguide exceeds 200 μm, even ifthe mode number is increased, the probability that light is madeincident on the optical switch with its one mode taken in an ON state isreduced. FIG. 13 shows the calculation result shown in FIG. 12 as anefficiency in a system. In this figure, the ordinate designates anefficiency in the system, and the abscissa designates a thickness “d” ofan optical waveguide. A curve showing a dependence of the thickness ofthe optical waveguide on the efficiency is inclined rightward, downward.This means that the efficiency becomes low as the thickness “d” of theoptical waveguide becomes large, and more specifically, the probabilitythat light of each mode is made incident on one optical switch isreduced as the thickness “d” of the optical waveguide becomes large.

[0060] Based on the above-described relationship, an optimum thicknessof an optical waveguide for increasing the light intensity can bedetermined. Assuming that a length of a function layer functioning as aswitching portion in the longitudinal direction of an optical waveguideof an optical switch is set to 1 mm, the optimum thickness of theoptical waveguide becomes a value in a range of 50 to 200 μm. Namely, ifthe thickness of the optical waveguide is excessively small, since themode number is decreased, it is difficult to obtain a sufficient lightintensity. Reversely, if the thickness of the optical waveguide isexcessively large, since the probability that laser light is madeincident on one liquid crystal switch as an optical switch is reduced,the light intensity is also lowered.

[0061] A thickness of an optical waveguide can be generalized withrespect to a size of an optical switch For example, letting L μm be alength of a function layer of an optical switch in the longitudinaldirection of the optical waveguide, the thickness of the opticalwaveguide suitable for realizing a high light emergence efficiency canbe set in a range of 0.05·L μm to 0.2·L μm. If the length L μm of thefunction layer is set to 1,000±300 μm, the excellent light emergenceefficiency, which corresponds to the above-described calculation result,can be obtained.

[0062] The function layer of the optical switch in this embodiment isone kind or a combination of two or more kinds selected from a groupconsisting of layers capable of, depending on a change in electric fieldor light, modulating a refractive index, a refractive indexdistribution, an emission intensity, a color density, a dielectricconstant, and a permeability, and layers capable of, depending on achange in electric field or light, changing a liquid crystal alignmentstate, and scattering light. Such a device having a function layerallows selective emergence or cutoff of light. In particular, in thecase of using the liquid crystal device 3 as the device having afunction layer of the optical switch as in this embodiment, the liquidcrystal device 3 may be desirable to have ferroelectric liquid crystal.The length of the function layer is an effective size for emergence andcutoff of light from the optical waveguide, and if a frame or the likeis formed at an end portion of the function layer, a size of a portionof the function layer inside the frame becomes the length L used fordetermining the optimum thickness of the optical waveguide.

[0063] One of application examples of the present invention is a displayunit using the above-described optical waveguides. If refractive indexesof respective optical switch are non-uniform, a light emergenceefficiency is varied, with a result that there occurs an unevenluminance. According to the present invention, however, even if theremay occur such a non-uniformity between the refractive indexes ofadjacent two of the optical switches, since the light emergenceefficiency is kept constant, it is possible to eliminate the occurrenceof an uneven luminance.

[0064] As another application example, an optical switch of the presentinvention can be used for an optical communication field. In acomplicated optical switch accompanied by parallel processing, even whena single signal is inputted, a multiple signals may be often outputted.For example, in the case where a plurality of optical switches areprovided on one optical waveguide, if an efficiency of one opticalswitch is different from that of another optical switch, a signalintensity may be varied, tending to cause an error. According to thepresent invention, such a problem can be solved. The present inventionis applicable not only to display units and optical communication unitsbut also to centralized light emitting computing devices,two-dimensional computers, or other units on which a plurality ofoptical switches are arrayed.

[0065] As described above, according to the optical switch and thedisplay unit using the optical switches in accordance with the presentinvention, since a small change region, in which a light emergenceefficiency is not largely changed even if a thickness and a refractiveindex of a film are varied, is utilized, it is possible to easilyrealize uniformity of the light emergence efficiency, and since athickness of an optical waveguide is optimized with respect to a size ofan optical switch, it is possible to improve the light emergenceefficiency and hence to realize a high-intensity output.

[0066] While the preferred embodiments of the present invention havebeen described using the specific terms, such description is forillustrative purposes only, and it is to be understood that changes andvariations may be made without departing from the spirit or scope of thefollowing claims.

What is claimed is:
 1. An optical switch for making part of incidentlight, which contains a specific polarized light component and has beenmade incident on an optical waveguide, selectively emergent from saidoptical waveguide to a light emergence portion provided outside saidoptical waveguide, said optical switch comprising: a multi-layerstructure composed of a plurality of light transmissive layer; whereinletting σ be a refractive index control accuracy at the time ofproducing said multi-layer structure, a refractive index of at least onelight transmissive layer in said multi-layer structure is different froma refractive index of a light transmissive layer other than said atleast one light transmissive layer in said multi-layer structure by 3 σor more.
 2. An optical switch according to claim 1, wherein said atleast one light transmissive layer having a different refractive indexis either of inner layers, excluding the uppermost layer and thelowermost layer, of said multi-layer structure.
 3. An optical switch formaking part of incident light, which contains a specific polarized lightcomponent and has been made incident on an optical waveguide,selectively emergent from said optical waveguide to a light emergenceportion provided outside said optical waveguide, said optical switchcomprising: a light transmissive stacked structure including a functionlayer for selective emergence of said incident light; wherein letting Δnbe a difference between a refractive index n₀ of said optical waveguideand a refractive index n₁ of an arbitrary layer forming part of saidstacked structure, “d” be a thickness of said arbitrary layer, and λ bea wavelength of said incident light, the values of Δn, “d”, and λsatisfy a condition of 2.20×10⁻³≦|Δn·d·λ⁻¹|≦3.03×10⁻³.
 4. An opticalswitch according to claim 3, wherein said optical waveguide has arefractive index ranging from 1.57 to 1.60; and said light transmissivestacked structure contains at least one layer disposed on said opticalwaveguide, said at least one layer having a refractive index rangingfrom 1.594 to 1.595 and a thickness ranging from 0.13 μm to 0.16 μm. 5.An optical switch according to claim 3, wherein said optical waveguidehas a refractive index ranging from 1.57 to 1.60; and said lighttransmissive stacked structure contains two layers disposed on saidoptical waveguide, said two layers each having a refractive indexranging from 1.594 to 1.595 and a thickness ranging from 0.13 μm to 0.16μm.
 6. An optical switch according to claim 3, wherein said lighttransmissive stacked structure contains a transparent resin layer.
 7. Anoptical switch according to claim 6, wherein said transparent resinlayer is made from a polyimide based resin.
 8. An optical switchaccording to claim 3, wherein said light transmissive stacked structurecontains a transparent electrode layer.
 9. An optical switch accordingto claim 3, wherein said optical waveguide is made from a polycarbonatebased resin.
 10. An optical switch according to claim 3, wherein saidfunction layer is composed of one kind or two or more kinds of layersselected from a group consisting of layers capable of, depending on achange in electric field or light, modulating a refractive index, arefractive index distribution, an emission intensity, a color density, adielectric constant, and a permeability, and layers capable of,depending on a change in electric field or light, changing a liquidcrystal alignment state, and scattering light.
 11. An optical switchaccording to claim 3, wherein said function layer is a ferroelectricliquid crystal, and is held between a pair of transparent resin layers.12. An optical switch according to claim 3, wherein said incident lightis light emitted from a semiconductor laser or a light emitting diode.13. A display unit comprising: a plurality of optical waveguides,disposed approximately in parallel to each other, for receiving lightcontaining a specific polarized light component as incident light; oneor two or more light emergence portions crossing said opticalwaveguides; and optical switches, disposed between said waveguides andsaid light emergence portions, for making part of said incident lightselectively emergent from said optical waveguides to said lightemergence portions provided outside said optical waveguides; whereineach of said optical switches has a light transmissive stacked structureincluding a function layer for selective emergence of said incidentlight; and letting Δn be a difference between a refractive index n₀ ofsaid optical waveguide and a refractive index n₁ of an arbitrary layerforming part of said stacked structure, “d” be a thickness of saidarbitrary layer, and λ be a wavelength of said incident light, thevalues of Δn, “d”, and λ satisfy a condition of2.20×10⁻³≦|Δn·d·λ⁻¹|≦3.03×10⁻³.
 14. A display unit according to claim13, wherein said light transmissive stacked structure contains atransparent resin layer.
 15. A display unit according to claim 14,wherein said transparent resin layer is made from a polyimide basedresin.
 16. A display unit according to claim 13, wherein said lighttransmissive stacked structure contains a transparent electrode layer.17. A display unit according to claim 13, wherein said optical waveguideis made from a polycarbonate based resin.
 18. A display unit accordingto claim 13, wherein said function layer is composed of one kind or twoor more kinds of layers selected from a group consisting of layerscapable of, depending on a change in electric field or light, modulatinga refractive index, a refractive index distribution, an emissionintensity, a color density, a dielectric constant, and a permeability,and layers capable of, depending on a change in electric field or light,changing a liquid crystal alignment state, and scattering light.
 19. Adisplay unit according to claim 13, wherein said function layer is aferroelectric liquid crystal, which is held between a pair oftransparent resin layers.
 20. A display unit according to claim 13,wherein said incident light is light emitted from a semiconductor laseror a light emitting diode.
 21. A display unit according to claim 13,wherein light emitting devices functioning as red light sources, bluelight sources, and green light sources are sequentially arrayed so as tobe aligned with said optical waveguides; and each of said light emittingdevices is controlled to emit light in response to a specific signal,and the light emitted from said light emitting device is made incidenton the corresponding one of said optical waveguides as said incidentlight.
 22. A display unit comprising: optical switches adjacent to eachother; wherein each of said optical switches, which is different fromthat adjacent thereto in terms of at least one of a thickness and arefractive index of a layer forming said optical switch, is provided soas to correspond to a wavelength of light emitted from each lightemitting device.
 23. An optical switch for making part of incidentlight, which contains a specific polarized light component and has beenmade incident on an optical waveguide, selectively emergent from saidoptical waveguide to a light emergence portion provided outside saidoptical waveguide, said optical switch comprising: a light transmissivestacked structure including a function layer for selective emergence ofsaid incident light; wherein letting L μm be a length of said functionlayer in the longitudinal direction of said optical waveguide, athickness of said optical waveguide is in a range of 0.05·L μm to 0.2·Lμm.
 24. An optical switch according to claim 23, wherein the length L μmof said function layer is 1,000±300 μm.
 25. A display unit comprising: aplurality of optical waveguides, disposed approximately in parallel toeach other, for receiving light containing a specific polarized lightcomponent as incident light; one or two or more light emergence portionscrossing said optical waveguides; and optical switches, disposed betweensaid waveguides and said light emergence portions, for making part ofsaid incident light selectively emergent from said optical waveguides tosaid light emergence portions provided outside said optical waveguides;wherein each of said optical switches has a light transmissive stackedstructure including a function layer for selective emergence of saidincident light; and letting L μm be a length of said function layer inthe longitudinal direction of said optical waveguide, a thickness ofsaid optical waveguide is in a range of 0.05·L μm to 0.2·L μm.
 26. Adisplay unit according to claim 25, wherein the length L μm of saidfunction layer is 1,000±300 μm.
 27. An optical switch for making part ofincident light, which contains a specific polarized light component andhas been made incident on an optical waveguide, selectively emergentfrom said optical waveguide to a light emergence portion providedoutside said optical waveguide, said optical switch comprising: a lighttransmissive stacked structure including a function layer for selectiveemergence of said incident light; wherein letting Δn be a differencebetween a refractive index n₀ of said optical waveguide and a refractiveindex n₁ of an arbitrary layer forming part of said stacked structure,“d” be a thickness of said arbitrary layer, and λ be a wavelength ofsaid incident light, the values of Δn, “d”, and λ satisfy a condition of|Δn·d·λ⁻¹|≦3.03×10⁻³ and |Δn·d·λ⁻¹|≠0.